WO2001070637A1

WO2001070637A1 - Method for direct clarification of ground water polluted with nitrate

Info

Publication number: WO2001070637A1
Application number: PCT/JP2001/002362
Authority: WO
Inventors: Masatoshi Matsumura; Rey Nayve Fidel
Original assignee: Japan Science And Technology Corporation
Priority date: 2000-03-24
Filing date: 2001-03-23
Publication date: 2001-09-27
Also published as: EP1270517A4; US6926831B2; JP2001269699A; KR20030040198A; EP1270517A1; KR100456749B1; US20040084376A1

Abstract

A method for direct clarification of a ground water polluted with nitrates, which comprises providing a biodegradable plastic derived from starch and usable both as a single carbon source and as a carrier for immobilizing bacterial bodies, immobilizing denitrifying bacteria on the carrier, and contacting the resulting immobilized bacteria with a ground water polluted with nitrate nitrogen; and an apparatus for practicing the method. The method allows the use of a carbon source with high efficiency and the densification of denitrifying bacteria, and thus can be used for clarifying a ground water directly with high safety, with no need for the addition of a heavy metal.

Description

Specification

Method for direct purification of groundwater contaminated with nitric acid

The invention of the present application relates to a method and an apparatus for directly purifying nitric acid-contaminated groundwater. More specifically, the invention of this application relates to an efficient, safe and inexpensive direct purification method of groundwater for drinking and irrigation, etc., contaminated with nitrate nitrogen. Background art

In biological denitrification, a carbon source that is in the form of an electron donor is indispensable.For conventional nitrate contamination, that is, direct purification of groundwater contaminated with nitrate nitrogen, denitrifying bacteria and a water-soluble carbon source are required. Separately, they have been separately injected into groundwater. However, such a conventional method has a problem in that the denitrifying bacteria and the water-soluble carbon source easily diffuse into the groundwater vein and cannot be effectively used for filling.

In addition, in the case of denitrification for drinking, the carbon source to be used must avoid those that are toxic, such as methanol, and the selected carbon source is also restricted. Was.

Furthermore, since many of the enzymes involved in the denitrification metabolism process are metalloenzymes, it has heretofore been necessary to use trace amounts of heavy metals such as Fe, o, Mn, and Cu in order to fully demonstrate the ability of denitrifying bacteria. Addition has been required. However, there is a problem that the metal content of groundwater varies, and those with high metal content are not generally used for drinking.

Therefore, the invention of the present application solves the above-mentioned problems of the prior art, and enables efficient use of a carbon source and high concentration of denitrifying bacteria. It is an object of the present invention to provide a new purification method and a device for directly purifying groundwater with higher safety without adding heavy metals. Disclosure of the invention

The invention of the present application solves the problems as described above. First, a biodegradable plastic derived from starch is used as a single carbon source and a carrier for immobilizing cells. Provided is a method for directly purifying nitrate-contaminated groundwater, which is fixed and brought into contact with groundwater contaminated with nitrate nitrogen.

Also, the invention of this application is characterized in that, second, the above-mentioned direct purification method in which the starch content of the biodegradable plastic derived from starch is 60% by weight or more; Fourthly, the present invention provides the above-mentioned direct purification method in which the conductive plastic is porous, and fourthly, the above-mentioned direct purification method in which the porosity of starch-derived biodegradable plastic is 10% or more.

Furthermore, the invention of the present application is, fifthly, that biodegradable plastics derived from starch have low solubility in water; and sixth, biodegradable plastics derived from starch are waste products. Is provided as an embodiment of the direct purification method.

Seventh, the invention of the present application is directed to the direct purification method, wherein the denitrifying bacterium exhibits a denitrifying ability at a low temperature of 20 ° C or less without requiring heavy metals and without accumulating nitrous acid. I will provide a.

Eighth, the invention of the present application provides a direct purification method in which the cell-immobilized carrier is filled in a net case, and this is shaken up and down to make contact with water. Ninth, the direct purification method A direct purification device for nitric acid-contaminated groundwater, comprising a mesh case for storing and filling the carrier at least and a rocking means for rocking it vertically when it comes into contact with groundwater. Do, brief description of the drawings

FIG. 1 is a schematic diagram showing an example of the device configuration of the present invention.

FIG. 2 is a diagram exemplifying a result of the denitrification treatment as an example. BEST MODE FOR CARRYING OUT THE INVENTION

The invention of this application has the features as described above, and embodiments thereof will be described below.

Above all, the invention is characterized by the direct purification of groundwater contaminated with nitrate nitrogen by immobilizing denitrifying bacteria capable of growing starch as a single carbon source on inexpensive biodegradable plastic derived from starch. In this direct purification method, since the denitrifying bacteria are always present together with the carbon source, efficient use of the carbon source and high concentration of the denitrifying bacteria can be achieved. In addition, starch has no danger of toxicity as in the case of using methanol as a carbon source, and there are many microorganisms that can utilize the same, which is advantageous for separating useful denitrifying bacteria.

As the biodegradable plastic derived from starch, those having a starch content of 60% by weight or more, for example, about 70% by weight, having low solubility in water and being porous are preferably used. These properties are important factors in immobilizing large numbers of denitrifying bacteria and enabling relatively long-term treatment.

Examples of physical properties of suitable starch-derived biodegradable plastics For example, those having a specific gravity of 1.01 to 1.05, easily suspended, and having a porosity of 0 to 60% are exemplified. The raw material for starch may be various substances such as potato, sweet potato, wheat, corn and the like. Further, starch having an unsaturated bond such as methyl acrylate and the like which is subjected to repolymerization with a monomer having good polymerizability is also suitably used in the invention of this application.

Examples of biodegradable plastics derived from starch include those obtained by compounding or copolymerizing starch with lactic acid polymer, those subjected to crosslinking (polymerization) treatment with cyclodextrin, etc., and various other natural polymers. Various types such as those formed by complexation are _{used.t Since} they are used not only as a carrier for immobilizing cells but also as a single carbon source, starch or starch in biodegradable plastics is used. The proportion of the block is preferably at least 60% by weight. Further, from the viewpoint of immobilizing the cells in a larger amount and increasing the contact area with water, the biodegradable plastic is porous, more preferably has a porosity of 10% or more, and more preferably 15 to 50%. It is preferable to be about 45%.

In addition, as the starch-derived biodegradable plastic, a disposable substance actually used as a packing material or the like, that is, a recycled product of waste can also be used. In this case, the direct purification method of the present invention is extremely inexpensive. It is also significant from the viewpoint of effective use of waste.

For example, in the method of the present invention using a biodegradable plastic as a carrier, denitrifying bacteria are immobilized on the carrier. For immobilization of the bacteria, for example, it is only necessary to put a dried carrier into the suspension of the bacteria, and the bacteria are sucked into the pores of the carrier and easily fixed. in this case Various types of denitrifying bacteria can be selected from those of the genus Pseudomonas H ^ Janthinobacterium. Zoogloe, Alcal igenes H _¾ Ni trobacter. Nitrosomonas, Klebsiel la and the like. Specifically, Pseudomonas aeruginosa, Pseudomonas stutzer i, Pseudomonas mephitica, Janth i nobacterium um I ivi dum, Zoogloea sp., Alcal igenes den itrifi cans. Preferably, the bacterium exhibits a denitrifying ability without adding a heavy metal. In addition, since well water has a temperature of around 15 ° C, it is generally desirable that it has the ability to proliferate and denitrify at low temperatures of 20 ° C or less.

In the above-mentioned selection of denitrifying bacteria, for example, as exemplified in the Examples, the cells are transplanted into a GiItay-Starch medium, and those in which gas generation is observed can be determined as those having despair. In addition, the influence of heavy metals can be easily determined.

When the above-mentioned cells immobilized on starch-derived biodegradable plastics are introduced into the groundwater vein without using the method of the invention of the present application to cause secondary contamination, the effect is further improved. In order to exert the effect, it is desirable to put a considerably large amount of immobilized cells into the water vein. Therefore, the present invention also provides an apparatus for purifying nitric acid-contaminated groundwater in a well.

In such a device, a large amount of nitrogen gas is generated along with the activation of the denitrifying bacteria, and this gas adheres to the carrier and floats the carrier, so that the contact between the carrier and water is poor and the treatment efficiency is reduced. The problem of the occurrence of the problem can be predicted. Therefore, in the apparatus of the present invention, in order to prevent such a problem from occurring, the carrier is dispersed in water in a narrow well without crushing a fragile carrier having a small physical strength. For this reason, for example, as shown in Fig. 1, the inside of a cylindrical mesh basket (A) The cage is filled with 60 to 70% of the immobilized carrier (B) in the cage volume, and this is vertically moved by a vertical rocking means such as an air cylinder (C). At that time, for example, when moving down, move relatively slowly, and when moving up, move quickly. Such movement of the cage causes the internal carrier to rise in the water by buoyancy and maintain good contact with the water. Since the carrier is consumed as the denitrification progresses and needs to be replenished, the cage filled with the carrier should be a cartridge type. At the time of replacement, the carrier in the old cartridge can be mixed into the new cartridge. By this operation, the denitrifying bacteria attached to the old carrier can be newly transferred to the carrier and denitrified again.

Therefore, examples are shown below, and the method of the present invention will be described in more detail. Of course, the present invention is not limited by the following embodiments. Example

The denitrifying bacteria were isolated from the sediment of the lake. The source of the bacteria is the bottom mud of Senba Lake, Mito City. The separation method is as follows.

That is, a well-diluted bottom mud suspension is applied to a growth agar plate, cultured at 4 ° C for 3 to 4 weeks, and the resulting colonies are agar plates containing soluble starch (containing peptone and yeast extract). And cultured at 4 ° C for 3 to 4 weeks. Starch degradation by the generated colonies was confirmed by injecting a solution of potassium iodide and potassium iodide onto the plate, and by confirming that no black blue color appeared around the colonies. Colonies whose starch degradability was confirmed were transferred again to a starch-containing agar medium containing no peptone and yeast extract. The plants were planted and confirmed to grow on minimal nutrient media with only starch being the sole carbon source.

The 25 strains that passed this test were examined for their ability to denitrify.

The colony was transplanted to a test tube containing 20 ml of a Gay-Starch medium and cultured for 10 days. When the green color of the medium changed to blue and gas generation was observed, it was determined that the medium had denitrification ability, and a strain having high denitrification ability was obtained.

Analysis of the isolated strain using 16S rRNA revealed a high homology (98.12%) based on BLAST Search Data and was determined to be /.

In addition, the bacterium converted high-concentration nitric acid (350 ppm) to nitrogen gas at a low temperature of 15 ° C and without heavy metal addition without accumulating nitrite. This bacterium also had the property that the addition of heavy metals and the temperature of 30 ° C inhibited the denitrification ability.

Denitrifying bacteria 2>

By the same determination method as in the case of the aforementioned denitrifying bacterium 1, Pseudomonas mephi tica has a higher denitrifying capacity than Pseudomonas genus, does not require heavy metals, and does not accumulate nitrite at a temperature of 20 ° C or less. Denitrifying bacteria showing denitrification ability were selected.

Denitrifying bacteria 3>

According to the same method as that of Denitrifying Bacterium 2, a denitrifying bacterium was selected from Janthinobacterium genus of the genus Janthinobacterium.

The denitrification treatment in the simulated well in the laboratory was performed using the device with the configuration shown in Fig. 1.

The volume of the stainless steel basket (A) was set at 20% of the volume of the reactor calf. The mesh basket (A) was filled with a carrier (B) on which the above-mentioned cells were immobilized. As a carrier and a carbon source, waste of a starch-derived porous biodegradable plastic (starch content: 72% by weight), which is practically used as a packing material, was reused.

It has a specific gravity of 1.03 and a porosity of 20%. The carrier was added to the suspension of the cells to immobilize the cells.

Figure 2 shows the results over time of the test by the repetitive batch method of the denitrification treatment. The arrow in the figure means that new sodium nitrate was added. And nitrogen N 0 ₃ states, shows changes of nitrogen N 0 ₂ state.

In FIG. 2, the nitric acid did not decrease after the addition on the 17th day (17 to 23 days), because the starch carrier added at the start of the experiment was completely consumed. . A new starch carrier was added on the 23rd day, and despairing resumed.

Furthermore, as shown in Fig. 2, it was confirmed that 170 ppm of nitrate nitrogen could be completely removed at a low temperature of 15 ° C in 4 to 5 days without accumulating nitrous acid. . It was also shown that long-term denitrification can be achieved by replenishing the spent carrier.

In the case of denitrifying bacteria 2 and 3, 40 ppm and 150 ppm of nitrate nitrogen were completely removed at a low temperature of 15 ° C in 4 to 5 days without accumulating nitrite. It was confirmed that it was possible, and almost the same results as above were obtained. Industrial applicability

As described in detail above, in the invention of this application, denitrifying bacteria capable of growing with starch as a single carbon source are immobilized on inexpensive starch-derived biodegradable plastics to directly purify nitrate-nitrogen-contaminated groundwater. Therefore, the denitrifying bacteria are always present together with the carbon source, and efficient use of the carbon source and high concentration of the denitrifying bacteria can be achieved. Starch does not have the danger of toxicity unlike methanol as a carbon source.

Therefore, the invention of this application makes it possible to directly purify nitrate-contaminated groundwater efficiently and at a low cost without concern about toxicity.

Claims

Claims. A biodegradable plastic derived from starch is used as a single carbon source and a carrier for immobilizing cells, and a denitrifying bacterium is immobilized on the carrier and brought into contact with groundwater contaminated with nitrate nitrogen. Direct purification method for nitrate-contaminated groundwater.

The direct purification method according to claim 1, wherein the starch-derived biodegradable plastic has a starch content of 60% by weight or more.

3. The direct purification method according to claim 1, wherein the biodegradable plastic derived from starch is porous.

4. The direct purification method according to claim 3, wherein the biodegradable plastic derived from starch has a porosity of 10% or more.

The direct purification method according to any one of claims 1 to 4, wherein the starch-derived biodegradable plastic has low solubility in water.

The direct purification method according to any one of claims 1 to 5, wherein the starch-derived biodegradable plastic is reused waste.

The direct purification method according to any one of claims 1 to 6, wherein the denitrifying bacterium does not require heavy metals, does not accumulate nitrous acid, and exhibits a denitrifying ability at a low temperature of 20 ° C or less.

The direct purification method according to any one of claims 1 to 7, wherein the netting case is filled with a carrier, and this is swung up and down to make contact with water.

9. The apparatus for a direct purification method according to claim 8, further comprising: a mesh case for storing and filling the carrier, and a swinging means for swinging the mesh case up and down in a state of contact with groundwater. Features A direct purification device for nitric acid-contaminated groundwater.